Electro-optical devices include electronic, optical or electro-optical packages, integrated circuits, integrated optical circuits, Vertical Cavity Surface Emitting Lasers (VCSELs), edge emitting lasers, Light Emitting Diodes (LEDs), or various types of photodetectors. In addition to these active devices, passive optics such as apertures, lenses, mirrors, spacers, attenuators, diffractive elements, birefringent plates, Faraday rotators and fiber connectors are commonly used in the growing field of electro-optical devices.
In the mass manufacture of electro-optical devices, it is desirable to make strips or arrays of devices and to laminate these devices with layers of other devices or passive materials. Then, after lamination is complete, it is often desirable to separate the individual devices. In this way, handling and assembling devices is done en masse and not individually. Laminations (analogous to the laminated wood product commonly called plywood) require that the material of which the layers is made be flexible, or otherwise one has the danger of warping or breakage.
Further, in terminating fiber optic or integrated optic arrays one may wish to employ strips or arrays of material and devices with features that must maintain optical alignment.
Micro-optical technology is characterized by the requirement of micron-level alignment tolerances in hybrid IC's.
For example, VCSELs are generally fabricated in wafer form in two-dimensional arrays. Such an array may need to be mated to an array of individual lenses generated in a different material, say by Reactive Ion Etching (RIE).
Due to long term variations in lithographic dimensions and due to variations in temperature, the materials that are being fabricated may not "line-up" all the way from one end to the other end of the strip or across a two-dimensional array; or, if they are forced to line up everywhere, there may be a build up of stress.
Exact matching of thermal expansions of dissimilar materials is generally not possible. For example, the approximate coefficients of expansion for amorphous SiO.sub.2, Quartz, Silicon, Rutile, and Garnet are 0, 7, 3.3, 7, and 9 ppm/.degree. C., respectively. Given a temperature range of 60.degree. C. and a length of 10 cm, a difference in expansion coefficient of only 4 ppm would produce an end-to-end misalignment of approximately 24 .mu.m. In practice, only 1 .mu.m misalignment can be tolerated in some applications.
The goal is to maintain the existence of strips, for purposes of easier handling, yet to make the strips flexible between regions of tight tolerance. For example, as shown in FIG. 17a, if the two parts (70) and (71) of a structure are to be mechanically registered using V-grooves (74), and if there are several (2-100, say) devices (71a)-(71d) having these V-grooves, manufactured in a continuous strip, then it is possible that the mechanical registration for any one or two devices (whose width may be only a few mm) will succeed, but that the many devices along the length of the strip will become progressively more unlikely to be in alignment. FIG. 17a exaggerates this misalignment for purposes of illustration.
In addition to the above problem, two-dimensional optical arrays can be made out of laminations of separately prepared materials where features on different levels of the laminate must remain precisely aligned even when the thermal expansion differs for each of the laminate materials or where there is a slight magnification error between layers.
Such slight dimensional imperfection is not sufficient to be a problem on any one array subsystem, but the ability to provide some flexibility of each group of features relative to the total array is required.